Optical pickup apparatus, optical data recording/reproducing apparatus, and optical data recording/reproducing method

ABSTRACT

An optical pickup apparatus used in an optical data recording/reproducing apparatus for reading/reproducing data on an optical recording medium, including a light source, a diffracting device configured to transmit a light beam and to diffract a light beam reflected from the optical recording medium, an optical device having a reflecting portion and a transmitting portion configured to reflect one part of the light beam emitted from the light source and to transmit another part of the light beam to the optical recording medium and from the optical recording medium, and a photodetecting device to detect the light beam from the optical recording medium for signal light detection, and the light beam reflected by the reflecting portion of the optical device for monitor light detection of the light source.

The present application contains subject matter disclosed in JapanesePatent Application No. 2000-065384 filed on Mar. 9, 2000 in the JapanPatent Office, to which the present application claims priority, and theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup apparatus used inoptical data recording/reproducing, and particularly to an opticalpickup apparatus having a relatively small size and high performance.

2. Discussion of the Background

Generally, in an optical pickup apparatus, a light beam emitted from asemiconductor laser diode of a light source is transmitted through adiffracting device, and the light beam is converted to a parallel lightby a collimating lens and is irradiated onto a surface of an opticalrecording medium by an objective lens. A light beam reflected from thesurface of the optical recording medium is returned via the same opticalpath as that of the irradiated light, is diffracted by the diffractiondevice, and is received on a photodetecting device so that signal lightdetection is executed.

During this signal light detection, unless intensity of the light beamfrom the semiconductor laser diode is constant, accurate signal lightdetection cannot be executed. Therefore, in conventional optical pickupapparatuses, the power of the emitted light beam has been monitored.

In one such optical pickup apparatus, in Japanese Patent No. 2543237 forexample, an optical disk apparatus is proposed which includes a laserlight emitting device serving as a light source, and a first opticaldevice which focuses a light emitted from the laser light emittingdevice on to a data recording surface serving as an optical disk. Asecond optical device includes a first region for generating a firstdiffracting light of a transmitting type hologram, which generates afirst diffracting light corresponding to a focusing error or a trackingerror in an optical pickup with respect to the data recording surface ofthe optical disk on the basis of a light reflected from the datarecording surface, and a second region for generating a seconddiffracting light of a reflection type hologram, the second region beingcoated on its surface by a film of a predetermined reflectance and whichgenerates a second diffracting light corresponding to a monitor light byreflecting and diffracting a part of the light emitted from the laserlight emitting device toward the data recording surface. A photodetectordetects the first and the second diffracting lights generated by thesecond optical device, and a focusing controlling device focuses thelight beam according to an output of the photodetector. A trackingcontrolling device tracks a predetermined position according to anoutput of the photodetector, and an output controlling device controlsan output of the laser light emitting device to a predetermined valueaccording to an output of the photodetector.

Namely, in the above described optical disk apparatus, the secondoptical device is provided with a first region for generating a firstdiffracting light which generates the first diffracting light,corresponding to a focusing error or a tracking error of an opticalpickup with respect to a data recording surface of the optical disk onthe basis of a light reflected from the data recording surface, and asecond region for generating a second diffracting light, the secondregion being coated on its surface by a film of a predeterminedreflectance and which generates a second diffracting light correspondingto the monitor light by reflecting and diffracting a part of a lightemitted from a laser emitting device toward the data recording surface.Further, the first diffracting light and the second diffracting lightwhich are generated in the second optical device are detected on aphotodetector, and the output of the laser light emitting device iscontrolled by using the output of the photodetector of this optical diskapparatus. Thereby, the optical pickup apparatus is made small in sizeand at low cost.

Also, a technique to increase light utilization efficiency and to obtaina signal of high signal to noise ratio by using a polarization hologramhas been proposed (see “HOE unit of high efficiency for DVD (2)” inApplied Physics Society in spring of 1998).

In this technique, signal light detection is executed by using apolarization hologram, and further a reflection hologram, which is not apolarization hologram but a general hologram and formed beside thepolarization hologram, for detecting a monitor light The reflectionhologram is formed on a board which is separate from the board of thepolarization hologram for signal light detection, and the two boards arealigned in position, pasted, and integrated to each other.

However, in such conventional techniques, in order to further reducesize and lower cost, and also to detect a signal further accurately,further improvement has been necessary.

Namely, in the optical disk apparatus disclosed in Japanese Patent No.2543227, the second optical device is provided with a first region forgenerating a first diffracting light of a transmitting type hologramwhich generates a first diffracting light corresponding to a focusingerror and a tracking error in an optical pickup with respect to a datarecording surface on the basis of the light reflected from an opticalrecording surface, and a second region, for generating a seconddiffracting light of a reflecting type hologram, which is coated on itssurface by a film of a predetermined reflectance and which generates asecond diffracting light corresponding to a monitor light by reflectingand diffracting a part of a light emitted from a laser light emittingdevice toward the data recording surface. If the optical pickupapparatus is configured such that a transmitting type hologram and areflecting type hologram are used for increasing the light utilizationefficiency and for obtaining a signal of high signal to noise ratio andboth holograms exist together on one board for reducing the cost of theapparatus, optimum processing can be executed only for one of theholograms. Therefore, there are problems in that light utilizationefficiency and accuracy of signal light detection are reduced.

Further, in the technique disclosed in the HOE unit of high efficiencyfor DVD (2), the signal light detection is executed by using apolarization hologram, and further a reflection hologram, which is not apolarization hologram but a general hologram and formed beside thepolarization hologram, for detecting a monitor light. With thistechnique, there are problems in that diffraction efficiency of amonitor light is about 20% atmost, and that flare light is large. Inaddition, because the reflection hologram is formed beside thepolarization hologram, and alignment of the positions of thepolarization hologram and the reflection hologram is required to beexecuted with high accuracy, the manufacturing efficiency is relativelylow, the size of an apparatus is relatively large, and the cost of theapparatus is relatively high.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an opticalpickup apparatus used in an optical data recording/reproducingapparatus, in which a signal light and a monitor light are guided to onephotodetecting device by using only a transmitting type diffractingdevice of a transmitting type hologram, and thereby light utilizationefficiency can be improved, and accuracy of monitor light detection andsignal light detection can be improved.

Another object of the present invention is to provide an optical pickupapparatus, which can be relatively small in size, simple in assemblingand low in cost, and in which monitor light detection and signal lightdetection can be more stable and accurate.

Another object of the present invention is to provide an optical pickupapparatus, in which diffracting efficiency of a diffracting device canbe improved, a flare light can be reduced, and monitor light detectionand signal light detection can be performed with increased sensitivity.

Another object of the present invention is to provide an optical pickupapparatus in which monitor lights with respect to light sources ofplural wavelengths are detected on one detecting device, and thereby acircuit can be relatively simple and low in cost, and accuracy ofmonitor light detection and signal light detection can be improved.

Another object of the present invention is to provide an optical pickupapparatus, in which a reflecting portion of an optical device with areflecting portion and a diffracting portion of a diffracting device areformed in positions corresponding to each Far Field Pattern (FFP) oflights of different wave lengths, and in which the diffracting devicecan be relatively simple in structure, and monitoring light detectionand signal light detection can be performed with increased sensitivity.

Another object of the present invention is to provide an optical pickupapparatus in which, with respect to each of light beams of pluralwavelengths, diffracting efficiency can be improved, flare light can bereduced, and monitor light detection and signal light detection can beperformed with increased sensitivity.

Another object of the present invention is to provide an optical pickupapparatus, in which intensity of a light beam which is guided to aphotodetecting device within diffracting lights of ± first order islarger, and signal to noise ratio of monitor light detection and signallight detection can be improved, and a flare light can be reduced.

Those and other objects and advantages are achieved by the presentinvention which provides an optical pickup apparatus forreading/reproducing data on an optical recording medium, including alight source configured to emit a light beam, a diffracting deviceconfigured to transmit the light beam emitted from the light source andto diffract a light beam reflected from the optical recording medium, anoptical device having a reflecting portion and a transmitting portion,configured to reflect one part of the light beam emitted from the lightsource to the diffracting device by the reflecting portion and totransmit another part of the light beam emitted from the light source tothe optical recording medium by the transmitting portion, and totransmit the light beam reflected from the optical recording medium tothe diffracting device by the transmitting portion, a photodetectingdevice configured to detect the light beam reflected from the opticalrecording medium through the optical device and the diffracting devicefor signal light detection, and wherein the diffracting device includesa diffracting portion to diffract the part of the light beam reflectedby the reflecting portion of the optical device to the photodetectingdevice, so as to be detected on the photodetecting device for monitorlight detection of the light source.

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with accompanying drawings,wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an optical pickup apparatus usedin an optical data recording/reproducing apparatus of one embodiment ofthe present invention;

FIG. 2 is a plan view illustrating an optical device of the apparatus inFIG. 1;

FIG. 3 is a plan view illustrating a diffracting device of the apparatusin FIG. 1;

FIG. 4 is a plan view illustrating a photodetecting device of theapparatus in FIG. 1;

FIG. 5 is a schematic view illustrating an optical pickup apparatusaccording to another embodiment of the present invention;

FIG. 6 is a schematic view illustrating an optical pickup apparatus ofFIG. 5 having two photodetecting devices;

FIG. 7 is a schematic view illustrating an optical pickup apparatus ofFIG. 5 having one photodetecting device;

FIG. 8 is a schematic view illustrating an optical pickup apparatusaccording to another embodiment of the present invention;

FIG. 9 is a schematic view illustrating an optical pickup apparatusaccording to another embodiment of the present invention;

FIG. 10 is a plan view illustrating a diffracting portion of the opticalpickup apparatus in FIG. 9;

FIG. 11 is a view illustrating one kind of optical pickup apparatus inFIG. 9;

FIG. 12 is a plan view illustrating another type of diffracting portionin FIG. 10;

FIG. 13 is a side view illustrating a diffracting device with areflecting portion in which a diffracting element and an optical elementwith a reflecting portion for monitor are integrated; and

FIG. 14 is a side view illustrating another diffracting device with areflecting portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-4 are views illustrating an optical pickup apparatus of a firstembodiment of the present invention.

FIG. 1 is a schematic view illustrating an optical pickup apparatus 1used in an optical data recording/reproducing apparatus of the firstembodiment of the present invention. The optical pickup apparatus 1 isprovided with a semiconductor laser diode 2 serving as a light source, adiffracting device 3, an optical device with reflecting portion formonitor 4, a collimating lens 5, an objective lens 6, and aphotodetecting device 7.

The semiconductor laser diode 2 and the photodetecting device 7 areformed on one board 8, and a light beam is emitted toward thediffracting device 3 by the semiconductor laser diode 2. The light beamemitted toward the diffracting device 3 is incident to the collimatinglens 5 through the diffracting device 3 and the optical device withreflecting portion for monitor 4.

In the optical device with reflecting portion for monitor (an opticaldevice with reflecting portion) 4, as illustrated in FIG. 2, areflecting portion 4 a is formed in its peripheral portion, and atransmitting portion 4 b is formed in its center portion. The opticaldevice with reflecting portion for monitor 4 transmits only a light beamwhich is incident to the transmitting portion 4 b of the center portionfrom the diffracting device 3 so as to be incident to the collimatinglens 5. The light beam which is incident to the reflecting portion 4 aof its peripheral portion is reflected toward the diffracting device 3.

The collimating lens 5 converts the incident light into a parallel lightso as to be incident to the objective lens 6. The objective lens 6focuses the light beam which is incident from the collimating lens 5 soas to be irradiated onto a data recording surface of an opticalrecording medium 10.

The light which is incident onto the optical recording medium 10 isdiffracted by a track formed on the data recording medium surface, andis then reflected as a reflected light to the objective lens 6. Thereflected light is incident to the collimating lens 5 through theobjective lens 6.

The reflected light which is incident to the collimating lens 5 isincident to the optical device with reflecting portion for monitor 4through the collimating lens 5, and further it is incident to thediffracting device 3 through the transmitting portion 4 b of the devicewith reflecting portion for monitor 4.

The diffracting device 3 is provided with a diffracting portion forsignal 3 a in its center portion, and a diffracting portion for monitor3 b in its peripheral portion, as illustrated in FIG. 3. Also, thediffracting device 3 is a transmitting type diffracting device of atransmitting type hologram.

In the diffracting device 3, the reflected light which is reflected fromthe optical recording medium 10 and which passes through the collimatinglens 5 and the optical device with reflecting portion for monitor 4, isincident onto the diffracting portion for signal 3 a. By the diffractingportion for signal 3 a, the reflected light from the optical recordingmedium 10 is diffracted and is made incident onto the photodetectingdevice 7. Also, the reflected light which is reflected on the reflectingportion 4 a of the optical device with reflecting portion for monitor 4is incident onto the diffracting portion for monitor 3 b of thediffracting device 3. By the diffracting portion for monitor 3 b, thereflected light from the reflecting portion 4 a of the optical devicewith reflecting portion for monitor 4 is diffracted so as to be incidentonto the photodetecting device 7.

In the photodetecting device 7, a photodetecting portion for signallight detection 7 a and a photodetecting portion for monitor lightdetection 7 b are arranged in respective regions of the photodetectingdevice 7, as illustrated in FIG. 4. To the photodetecting portion forsignal light detection 7 a, the light beam which is diffracted in thediffracting portion for signal 3 a of the diffracting device 3 isincident, and to the photodetecting portion for monitor light detection7 b, the light beam which is diffracted in the diffracting portion formonitor 3 b of the diffracting device 3 is incident, respectively.

The photodetecting portion for signal light detection 7 a and thephotodetecting portion for monitor light detection 7 b detect theincident light beams, and output signals corresponding to the propertiesof the detected lights, receptively.

Next, the function of the above described embodiment will be described.In the optical pickup apparatus 1 of this embodiment, a light beamemitted from the semiconductor laser diode 2 passes through thediffracting device 3 and the transmitting portion 4 b of the opticaldevice with reflecting portion for monitor 4, and is incident onto thecollimating lens 5. The light beam is converted to a parallel light beamby the collimating lens 5 so as to be incident onto the objective lens6. The light beam, which is incident onto the objective lens 6 from thecollimating lens 5, is irradiated by the objective lens 6 onto a datarecording surface of the optical recording medium 10. The reflectedlight, which is diffracted and reflected on the data recording surfaceof the optical recording medium 10, passes through the objective lens 6and the collimating lens 5, which are installed on the same optical pathas that of the light from the light source 2 toward the opticalrecording medium, so as to be incident onto the optical device withreflecting portion for monitor 4.

In the optical pickup apparatus 1, the reflected light, which isincident onto the optical device with reflecting portion for monitor 4,passes through the transmitting portion 4 b so as to be incident ontothe diffracting portion for signal 3 a of the diffracting device 3. Thelight which is reflected from the optical recording medium 10 isincident onto the detecting portion for signal light detection 7 a ofthe photodetecting device 7 by the diffracting portion for signal 3 a asthe light beam for signal, and the light beam for signal is detected onthe photodetecting portion for signal light detection 7 a of thephotodetecting device 7.

Additionally, in the optical pickup apparatus 1, the optical device withreflecting portion for monitor 4 is provided with the reflecting portion4 a in its peripheral portion. The light beam emitted from thesemiconductor laser diode 2, which passes through the diffracting device3 and which is incident to the reflecting portion 4 a formed in theperipheral portion of the optical device with reflecting portion formonitor 4, is reflected on the reflecting portion 4 a to the diffractingportion for monitor 3 b of the diffracting device 3. The light beam,which is reflected to the diffracting portion for monitor 3 b, isincident onto the photodetecting portion for monitor light detection 7 bof the photodetecting device 7 as a light beam for monitor, and thelight beam for monitor is detected by the photodetecting portion formonitor light detection 7 b. As described above, in the optical pickupapparatus 1 of this embodiment, when a light beam from the semiconductorlaser diode 2 serving as a light source is irradiated onto a recordingsurface of the optical recording medium 10 through the diffractingdevice 3 and a reflected light from the optical recording medium 10 isdiffracted by the diffracting device 3 so as to be focused andirradiated onto the photo detecting device 7. The reflecting portion 4 aof the optical device with reflecting portion for monitor 4 reflects apart of the light beam, which is emitted from the semiconductor laserdiode 2 and which passes through the diffracting device 3, to thediffracting device 3, and the diffracting portion for monitor 3 bdiffracts the light reflected from the device with reflecting portionfor monitor 4 to the photodetecting device 7.

Therefore, by using only a transmitting type diffracting device of atransmitting type hologram, a signal light from the optical recordingmedium 10 and a monitor light are both guided to the one photodetectingdevice 7. As a result, the light utilization efficiency and the accuracyof monitor light detection can be improved and further the accuracy ofsignal light detection can be improved.

FIG. 5 is a schematic view illustrating an optical pickup apparatusaccording to a second embodiment of the present invention. In thisembodiment, a diffracting element and an optical element with reflectingportion are integrated.

The optical pickup apparatus of this embodiment is substantially thesame as that of the first embodiment, and the same portions as those ofthe first embodiment are designated and described by the same referencenumerals.

In FIG. 5, an optical pickup apparatus 20 of this embodiment is providedwith a diffracting device with reflecting portion 21, and in thediffracting device with reflecting portion 21, a diffracting element 22and an optical element with reflecting portion for monitor 23 areintegrated.

A light beam emitted from the semiconductor laser diode 2 is incidentonto the diffracting element 22, and the diffracting element 22transmits the incident light beam to the optical element with reflectingportion for monitor 23.

In the optical element with reflecting portion for monitor 23, areflecting portion 23 a is formed in its peripheral portion and atransmitting portion 23 b is formed in its center. The reflectingportion 23 a reflects a light beam, which passes through the diffractingelement 22 and which is incident to the reflecting portion 23 a, towardthe diffracting element 22.

The diffracting element 22 has substantially the same structure as thatof the diffracting device 3 of the first embodiment, not illustrated inFIG. 5, and a diffracting portion for signal is formed in its centerportion and a diffracting portion for monitor is formed in itsperipheral portion. A light beam reflected by the reflecting portion 23a of an optical element with reflecting portion for monitor 23 isincident onto the diffracting portion for monitor of the diffractingelement 22, and the incident light is diffracted toward thephotodetecting device 7 by the diffracting portion for monitor. As inthe diffracting device 3 of the above described first embodiment, thelight beam which is reflected from the optical recording medium 10 andwhich passes through the transmitting portion 23 b of the opticalelement with reflection portion for monitor 23 is incident onto thediffracting portion for signal of the diffracting element 22. Therefore,the light beam is diffracted toward the photodetecting device 7 by thediffracting portion for signal of the diffracting element 22.

As described above, in the optical pickup apparatus 20, the diffractingelement 22 and the optical element with reflecting portion for monitor23 are integrated as the diffracting device with reflecting portion 21.

Therefore, the optical pickup apparatus 20 can be made relatively smallin size, and simpler to assemble. Further, stable and accurate signallight detection and monitor light detection can be achieved.

In this embodiment, a light beam for monitor which is reflected on thereflecting portion 23 a of the optical element with reflecting portionfor monitor 23, is diffracted by the diffracting portion for monitor ofthe diffracting element 22 so as to be incident onto the onephotodetecting device 7. However, two photodetecting devices 25 and 26can be arranged as illustrated in FIG. 6. The light beam for monitor,which is reflected on the reflecting portion 23 a of the peripheralportion of the optical element with reflecting portion for monitor 23,is divided into two parts by the diffracting portion for monitor of thediffracting element 22, and respective parts of the light beam arediffracted toward nearer one of the photodetecting devices 25 and 26 soas to be respectively detected by the photodetecting devices 25 and 26.In this case, a photodetecting portion for signal light detection and aphotodetecting portion for monitor light detection are both formed inone of the photodetecting devices 25 and 26, and only a photodetectingportion for monitor light detection is formed in the other of thephotodetecting devices 25 and 26. The light beam for signal which isreflected from the optical recording medium 10 and which is diffractedin the diffracting element 22, is incident onto one of thephotodetecting devices 25 and 26 in which both the photodetectingportion for signal light detection and the photodetecting portion formonitor light detection are formed.

Further, in FIG. 6, the two photodetecting devices 25 and 26 arearranged so that a light beam for monitor, which is reflected from thereflecting portion 23 a formed in the peripheral portion of the opticalelement with reflecting portion for monitor 23 and divided into twoparts by the diffracting portion for monitor of the diffracting element22, is incident onto the two photodetecting devices 25 and 26. However,as illustrated in FIG. 7, only one detecting device 27 may be arrangedas in the first embodiment. A reflecting portion 23 c is formed only ina predetermined area of the peripheral portion of the optical elementwith reflective portion for monitor 23 which is farther from thephotodetecting device 27, and the reflecting portion 23 c is not formedin the peripheral portion which is nearer to the photodetecting device27.

In this case, the light beam for monitor which is reflected from thereflecting portion 23 c of the optical element with reflecting portionfor monitor 23 is diffracted toward the photodetecting device 27 by thediffracting portion for monitor of the diffracting element 22, and thislight beam for monitor is detected on the photodetecting device 27.

Namely, in general, a diffracting device cannot diffract 100% of anincident light, and, for example a non-diffracting light (a transmittinglight) Ln, indicated by a dashed line in FIGS. 6 and 7, is more or lessgenerated within an incident light which is reflected from thereflecting portion 23 a. Because this non-diffracting light Ln is aradiating light, it may be incident onto the photodetecting devices 25and 26 as a flare light, and thereby cause detecting accuracy to bereduced.

On the other hand, as illustrated in FIG. 7, by arranging the reflectingportion 23 c only in a predetermined area of the peripheral portion ofthe optical element with reflecting portion for monitor 23 which isfarther from the photodetecting device 27, flare light effects can bereduced. Light is reflected from the reflecting portion 23 c by thediffracting portion for monitor of the diffracting element 22 toward thephotodetecting device 27. Because the non-diffracting light Lntransmitted through the diffracting portion for monitor, which is nearerto the reflecting portion 23 c of the diffracting element 22, is furtherapart from the photodetecting device 27, as illustrated in FIG. 7, thenon-diffracting light Ln can be prevented from being incident onto thephotodetecting device 27 as a flare light. Therefore, detecting accuracyof a light beam for monitor can be improved.

In FIG. 7, the position of the photodetecting device 27 may bedetermined in relation to the amount of a light beam for monitor, or anelectric system etc. of the optical pickup apparatus 20.

FIG. 8 is a view illustrating an optical pickup apparatus according to athird embodiment of the present invention. In this embodiment, apolarization hologram and a quarter wave plate are used as a diffractingelement, and further, the polarization hologram, the quarter wave plateand an optical element with reflecting portion for monitor areintegrated.

The optical pickup apparatus in this embodiment is substantially thesame as that of the first embodiment, and the same portions as those ofthe first embodiment are designated and described by the same referencenumerals.

In FIG. 8, an optical pickup apparatus 30 is provided with a diffractingdevice with reflecting portion 31, and in the diffracting device withreflecting portion 31, a polarization hologram 32, a quarter wave plate33, and an optical element with reflecting portion for monitor 34 areintegrated.

A light beam which is emitted from the semiconductor laser diode 2 isincident onto the polarization hologram 32. The light beam emitted fromthe semiconductor laser diode 2 is a linear polarization light. Thepolarization hologram 32 has a relatively high transmittance, and ittransmits a light beam of linear polarization emitted from thesemiconductor laser diode 2 nearly 100% so as to be incident to thequarter wave plate 33.

The quarter wave plate 33 converts a light beam which is incidentthereto from the polarization hologram 32 into a circular polarizationlight so as to be incident onto the optical element with reflectingportion for monitor 34.

In the optical element with reflecting portion for monitor 34, areflecting portion 34 a is formed only in a predetermined area which isfarther from the position of the photodetecting device 7, and theremaining area is a transmitting portion 34 b. The optical element withreflecting potion for monitor 34 transmits the light beam through itstransmitting portion 34 b, and the light beam is irradiated onto a datarecording surface of the optical recording medium 10 through thecollimating lens 5 and the objective lens 6 as in the first embodiment,and the reflected light which is reflected from the data recordingsurface of the optical recording medium 10 and which passes through theobjective lens 6 and the collimating lens 5 is incident onto the quarterwave plate 33 through the transmitting portion 34 b. A light beam whichis incident onto the reflecting portion 34 a is reflected to the quarterwave plate 33 as a light beam for monitor, as illustrated by an arrowsign in FIG. 8.

The quarter wave plate 33 converts an incident light beam into a linearpolarization light to be incident to the polarization hologram 32.

The polarization hologram 32 diffracts an incident light beam toward thephotodetecting device 7 so as to be detected on the photodetectingdevice 7.

The light beam which is incident onto the polarization hologram 32includes a light beam for signal which is reflected from the opticalrecording medium 10 and a light beam for monitor which is reflected onthe reflecting portion 34 a of the optical element with reflectingportion for monitor 34. From the polarization hologram 32, the lightbeam for signal is incident onto the photodetecting portion 7 a of thephotodetecting device 7 and the light beam for monitor is incident ontothe photodetecting portion for monitor 7 b of the photodetecting device7.

With respect to a light beam which is reflected from the opticalrecording medium 10 and which is incident onto the polarization hologram32, and a light beam which is reflected from the reflecting portion 34 aof the optical element with reflecting portion for monitor 34 and whichis incident to the polarization hologram 32, the polarization state isrotated 90 degrees. Therefore, transmittance of the polarizationhologram 32 is relatively low and diffraction efficiency is relativelyhigh. As a result, a light beam which is diffracted by the polarizationhologram 32 can be incident onto the photodetecting device 7 with arelatively high degree of efficiency (30% or more), and accuracy ofsignal light detection and monitor light detection can be improved.

Also, in the conventional technique described in “HOE unit of highefficiency for DVD (2)” in Applied Physics Society in spring of 1998, asdescribed above, signal light detection is executed by using apolarization hologram, however, monitor light detection is executed by ageneral reflection hologram, which is not a polarization hologram, inaddition to the polarization hologram for signal light detection.Therefore, there is a problem that a reflection hologram needs to beformed besides the polarization hologram. Further, there are problems inthat the diffraction efficiency of a monitor light is about 20% at most,and that the flare light is large. In addition, the alignment ofpositions between the polarization hologram and the reflection hologramneeds to be accurate, thereby decreasing the manufacturing productivity.Additionally, the size of an apparatus and the cost of an apparatus areincreased.

On the other hand, in the optical pickup apparatus 30 of thisembodiment, instead of a reflection hologram, the reflecting portion 34a of the optical element with reflecting portion for monitor 34 is used.Therefore, the manufacturing of an apparatus is relatively easy.Further, the alignment at high accuracy is not necessary because onlyreflection has to be done. Further, the diffraction efficiency can beimproved, and the flare light can be reduced because the monitoringlight is also diffracted by using the polarization hologram 32.

Especially, in the optical pickup apparatus 30 of this embodiment, thereflecting portion 34 a of the optical element with reflecting portionfor monitor 34 is only formed in a predetermined area in a positionapart from the photodetecting device 7. Therefore, the flare light canbe further prevented from being incident onto the photodetecting device7.

FIGS. 9-11 are views illustrating an optical pickup apparatus accordingto a forth embodiment of the present invention, in which the light beamsfor monitor are picked up from the light beams from two light sources oftwo different wavelengths.

The optical pickup apparatus in this embodiment is substantially thesame as that of the first embodiment, and the same portions as those ofthe first embodiment are designated In FIG. 9, an optical pickupapparatus 40 is provided with two semiconductor laser diodes 41 and 42,a diffracting device with reflecting portion 43, a photodetecting device44, and a collimating lens 5 and an objective lens 6 etc. which are notillustrated in the figure and which are substantially the same as thosein the first embodiment.

The semiconductor laser diodes 41 and 42 emit a light beam of awavelength (for example 650 or 635 nm) for a medium of a DVD system anda light beam of a wavelength (for example 780 nm) for a medium of a CDsystem toward a diffracting device with reflecting portion 43.

In the diffracting device with reflecting portion 43, a diffractingelement 45 and an optical element with reflecting portion for monitor 46are integrated, and light beams emitted from the semiconductor laserdiodes 41 and 42 are incident onto the diffracting element 45.

In the diffracting element 45, as illustrated in FIG. 10, a diffractingportion for signal 47 is formed in its center portion and a diffractingportion for monitor 48 is formed in its peripheral portion. In thediffracting portion for monitor 48, a hologram 49 for 650 nm (or 635 nm)and a hologram 50 for 780 nm wavelength light beams are formedalternatively.

In the optical element with reflecting portion for monitor 46, areflecting portion 46 a is formed only in a predetermined area of itsperipheral portion which is farther from the photodetecting device 44(the reflecting portion 46 a is not formed in its peripheral portionwhich is nearer to the photodetecting device 44), and a transmittingportion 46 b is formed in its center portion. In the optical elementwith reflecting portion for monitor 46, the light beams which areincident from the diffracting portion 45 to the transmitting portion 46b of its center portion are transmitted so as to be incident onto thecollimating lens 5, and the light beams which are incident onto thereflecting portion 46 a of its peripheral portion are reflected towardthe diffracting element 45.

The light beams which are reflected from the reflecting portion 46 a ofthe optical element with reflecting portion for monitor 46 are incidentonto the diffracting element 45, and the incident light beams arediffracted toward the photodetecting device 44 according to respectivewavelengths of the two light beams by the holograms 49 and 50 so thatthe two light beams are detected on the photodetecting device 44.

Next, the function of the above described embodiment will be described.As described above, the optical pickup apparatus 40 is provided with thesemiconductor laser diodes 41 and 42 which emit light beams of thewavelengths of a DVD system medium and that of a CD system medium inorder to record and reproduce data on both system mediums. For example,light beams of the wavelengths of 650 nm (or 635 nm) and 780 nm areemitted.

Of the light beams which are emitted from the semiconductor laser diodes41 and 42 and which are transmitted through the diffracting element 45of the diffracting device with reflecting portion 43, the light beamswhich are incident onto the reflecting portion 46 a of the opticalelement with reflecting portion for monitor 46 are reflected onto thediffracting element 45 as a light beam for monitor.

Referring now to FIG. 11, if the diffracting element 45 includes adiffracting portion 51 which has the same structure as the diffractingdevice 3 as illustrated in FIG. 3 and which corresponds to only one kindof wavelength, both light beams of two kinds of wavelengths which areemitted from the semiconductor laser diodes 41 and 42 cannot be detectedon the detecting device 44.

Namely, if the light beams which have different wavelengths arediffracted by one kind of a diffracting portion 51, they are focused ondifferent positions due to chromatic aberration. If the diffractingportion 51 corresponds only to one wavelength of the two light beams, asillustrated by a solid line in FIG. 11, the light beam of thecorresponding wavelength can be detected on the detecting device 44, butthe light beam of the other wavelength is focused on a position which isshifted from the photodetecting device 44, as illustrated by a dashedline in FIG. 11.

In this case, if the photodetecting device 44 has to be large, or twophotodetecting devices have to be arranged at positions corresponding todifferent wavelength, respectively, so that detection of the two lightbeams can be achieved. However, other problems occur such as that thesize of an optical pickup apparatus is increased and the cost isincreased.

However, in the optical pickup apparatus 40 of this embodiment, thediffracting element 45 has the diffracting portion for monitor 48 inwhich the hologram 49 for 650 nm (or 635 nm) and the hologram 50 for 780nm wavelengths are formed alternatively. Therefore, the light beams ofdifferent wavelengths which are emitted from the semiconductor laserdiodes 41 and 42 are diffracted to the photodetecting device 44 by theholograms 49 and so, respectively, so as to be detected on thephotodetecting device 44, as illustrated in FIG. 9.

Therefore, with respect to the semiconductor laser diodes 41 and 42 thatemit plural wavelengths, the monitor light signals can be detected byone detecting device 44, and thereby the circuit can be simple and thecost can be decreased. In addition, the accuracy of monitor lightdetection and the accuracy of signal light detection can be improved.

In this embodiment, although the holograms 49 and 50 in the diffractingportion for monitor 48 are alternatively formed around the circumferenceof the diffracting portion for signal 47, the forming method of the twokinds of holograms is not so limited. For example, as illustrated inFIG. 12, because the light beam is different in FFP (Far Field Pattern)which is the intensity distribution of a profile of a light beamaccording to the wavelength, the reflecting portions of the opticalelement with reflecting portion for monitor 46 may be formed only atpositions corresponding to FFP of each wavelength, and a hologram 53 anda hologram 54 for respective wavelengths of the two light beams may beformed at positions corresponding to the reflecting portions formed ascorresponding to the positions of the FFP. In a diffracting element 52in FIG. 12, the hologram 53 is for 650 nm (or 635 nm) and the hologram54 is for 780 nm wavelengths.

Thereby, the reflecting portion of the optical element with reflectingportion for monitor 46 and the holograms 53 and 54 of the diffractingelement 52 can be arranged at the positions which correspond to the FFPof the light beams of the different wavelengths, and therefore a simplestructure can be achieved. Further, signal light detection and monitorlight detection can be achieved with further increase in sensitivity.

In this embodiment, although the diffracting element 45 and the opticalelement with reflecting portion for monitor 46 are integrated in thediffracting device with reflecting portion 43, the diffracting element45 may be arranged so as to be apart from the optical element withreflecting portion for monitor 46 as in the first embodiment. However,by configuring the diffracting device with reflecting portion 43 suchthat the diffracting element 45 and the optical element with reflectingportion for monitor 46 are integrated as in this embodiment, the size ofan apparatus can be small made relative small. In addition, the portionsto be aligned are decreased so that the manufacturing productivity canbe improved.

Further, in this embodiment, although the diffracting device withreflecting portion 43 in which the diffracting element 45 and theoptical element with reflecting portion for monitor 46 are integrated isused, diffracting device with reflecting portion for monitor whichincludes a polarization hologram, a quarter wave plate and an opticalelement with reflecting portion for monitor can be also used.

FIGS. 13 and 14 are views illustrating an optical pickup apparatus of afifth embodiment, in which, the section form of a diffracting element isformed in a bilateral asymmetry, so that the amount of the light isincreased.

The optical pickup apparatus in this embodiment is substantially thesame as of the first embodiment, and the same portions as those of thefirst embodiment are designated and described by the same referencenumerals.

FIG. 13 is a side view illustrating a diffracting device with reflectingportion 60 which is used in the optical pickup apparatus according to afifth embodiment of the present invention. In the diffracting devicewith reflecting portion 60, a diffracting element 61 and an opticalelement with reflecting portion for monitor 62 are integrated.

A junction 63 between the diffracting element 61 and the optical elementwith reflecting portion for monitor 62 is formed at its section in ablaze form of a bilateral asymmetry In the optical element withreflecting portion for monitor 62, a reflecting portion 62 a is formedin its peripheral portion and a transmitting portion 62 b is formed inits center portion. A light beam emitted from the semiconductor laserdiode 2, not illustrated in FIG. 13, is incident onto the diffractingportion 61, and the incident light beam is transmitted to the opticalelement with reflecting portion for monitor 62 by the diffractingelement 61.

In the optical element with reflecting portion for monitor 62, a lightbeam which is incident onto the transmitting portion 62 b is irradiatedonto a data recording surface of the optical recording medium 10 throughthe collimating lens 5 and the objective lens 6, not illustrated in FIG.13. The reflected light from the optical recording medium 10 is incidentonto the optical element with reflecting portion for monitor 62 throughthe objective lens 6 and the collimating lens 5. The incident light beamis then transmitted to the diffracting element 61.

Further, in the optical element with reflecting portion for monitor 62,a light beam which is incident onto its reflecting portion 62 a isreflected from the reflecting portion 62 a toward the diffractingelement 61.

In the diffracting element 61, although not illustrated in FIG. 13, asin the diffracting device 3 of the first embodiment for example, adiffracting portion for signal is formed in its center portion and adiffracting portion for monitor is formed in its peripheral portion. Alight beam which is reflected from the reflecting portion 62 a of theoptical element with reflecting portion for monitor 62 is diffractedtoward the photodetecting device 7, not illustrated in FIG. 13, by thediffracting portion for monitor of the diffracting element 61. Also, alight beam which is reflected from the optical recording medium 10 andwhich is transmitted through the transmitting portion 62 b of theoptical element with reflecting portion for monitor 62 is incident ontothe diffracting portion for signal of the diffracting element 61, and isthen diffracted toward the photodetecting portion 7.

In the optical group apparatus of this embodiment, the junction 63between the diffracting element 61 and the optical element withreflecting portion for monitor 62 of the diffracting device withreflecting portion 60 is formed in blaze form, and a light beam formonitor which is reflected from the reflecting portion 62 a of theoptical element with reflecting portion for monitor 62 and a light beamfor signal which is transmitted through the transmitting portion 62 b ofthe optical element with reflecting portion for monitor 62 arediffracted and are incident onto the photodetecting device 7 by thejunction 63.

Therefore, a diffracting light which is not incident onto thephotodetecting device 7, for example high order lights of second orhigher order and one of ± first order lights, which are not guided tothe photodetecting device 7 can be decreased, and the other of the ±first order lights which are guided to the photodetecting device, can beincreased.

In this embodiment, although the junction 63 between the diffractingelement 61 and the optical element with reflecting portion for monitor62 is formed in a blaze form, as illustrated in FIG. 14, the form of thejunction is not so limited. For example, referring to FIG. 14, adiffracting device with reflecting portion 64 may be formed such thatthe diffracting portion 65 and an optical element with reflectingportion for monitor 66 are integrated and the section of junction 67between the diffracting element 65 and the optical element withreflecting portion for monitor 66 can be formed in a multi-level form ofbilateral asymmetry. In FIG. 14, in the optical element with reflectingportion for monitor 66, a reflecting portion 66 a is formed in itsperipheral portion and a transmitting portion 66 b is formed in itscenter portion. Thereby, the same technical advantages as describedabove can be also obtained.

Finally, technical advantages of different embodiments of the presentinvention will be described.

According to one aspect of the present invention, an optical pickupapparatus used in an optical data recording/reproducing apparatus forreading/reproducing data on an optical recording medium includes a lightsource configured to emit a light beam, a diffracting device configuredto transmit the light beam emitted from the light source, and todiffract the light beam reflected from the optical recording medium, anoptical device having a reflecting portion and a transmitting portion,configured to reflect one part of the light beam emitted from the lightsource to the diffracting device by the reflecting portion and totransmit the other part of the light beam emitted from the light sourceto the optical recording medium by the transmitting portion, and totransmit the light beam reflected from the optical recording medium tothe diffracting device by the transmitting portion, a photodetectingdevice configured to detect the light beam reflected from the opticalrecording medium through the optical device with reflecting portion andthe diffracting device for signal light detection, and wherein thediffracting device includes a diffracting portion to diffract the onepart of the light beam reflected by the reflecting portion of theoptical device with reflecting portion to the photodetecting device, soas to be detected on the photodetecting device for monitor lightdetection of the light source. Therefore, a signal light and a monitorlight are guided to one photodetecting device by using only atransmitting type diffracting device of a transmitting type hologram,and thereby light utilization efficiency and accuracy of monitor lightdetection and signal light detection can be improved. According toanother aspect of the present invention, in an optical pickup apparatus,the optical device with reflecting portion is integrated with thediffracting device. Therefore, the size of the apparatus can berelatively small, assembling of the apparatus can be simplified and thecost of the apparatus can be relatively low. Further, monitor lightdetection and signal light detection can be more stable and accurate.

According to another aspect of the present invention, in an opticalpickup apparatus, the diffracting device may include a polarizationhologram portion for monitor configured to diffract the light beamreflected from the optical device with reflecting portion to thephotodetecting device for monitor light detection. Therefore,diffracting efficiency can be improved, flare light can be reduced, andmonitor light detection and signal light detection can be performed withincreased sensitivity.

According to another aspect of the present invention, an optical pickupapparatus used in an optical data recording/reproducing apparatus forreading/reproducing data on an optical recording medium includesmultiple light sources configured to emit light beams of different wavelengths, a diffracting device configured to transmit the light beamsemitted from the light sources and to diffract the light beams reflectedfrom the optical recording medium, an optical device with reflectingportion having a reflecting portion and a transmitting portionconfigured to reflect one part of the light beams emitted from the lightsources to the diffracting device by the reflecting portion, and totransmit the other parts of the light beams emitted from the lightsources to the optical recording medium by the transmitting portion, andto transmit the light beams reflected from the optical recording mediumto the diffracting device by the transmitting portion, a photodetectingdevice, configured to detect the light beams reflected from the opticalrecording medium through the optical device with reflecting portion andthe diffracting device for signal light detection, and wherein thediffracting device includes plural diffracting portions, in which eachof the diffracting portions corresponds to one of the differentwavelengths, to diffract the respective one parts of the light beamsreflected by the reflecting portion of the optical device withreflecting portion to the photodetecting device, so as to be detected onthe photodetecting device for monitor light detection of each of thelight sources. Therefore, because monitor lights with respect to thelight sources of plural wavelengths are detected on one detectingdevice, a circuit can be simpler and cost can be lower, and accuracy ofmonitor light detection and signal light detection can be improved.

According to another aspect of the present invention, in an opticalpickup apparatus, wherein the reflecting portion of the optical devicewith reflecting portion includes plural reflecting portions arranged atpositions corresponding to the light beams of the plural wavelengths,and the plural diffracting portions of the diffracting device arearranged at positions corresponding to the plural reflecting portions ofthe optical device with reflecting portion respectively, and the lightbeams of different wavelengths reflected from the plural reflectingportions of the optical device with reflecting portion are diffracted bythe plural diffracting portions of the diffracting device to thephotodetecting device, so as to be detected on the photodetecting devicefor monitor light detection of each of the light sources. Therefore, areflecting portion of an optical device with reflecting portion and adiffracting portion of a diffracting device are formed in positioncorresponding to each FFP of lights of different wavelengths, and thediffracting device can be simpler in structure, and monitor lightdetection and signal light detection can be more sensitive.

According to another aspect of the present invention, in an opticalpickup apparatus, the optical device with reflecting portion isintegrated with the diffracting device. Therefore, size can be smaller,assembling ability can be simpler and cost can be lower, and monitorlight detection and signal light detection can be more stable andaccurate.

According to another aspect of the present invention, in an opticalpickup apparatus, the diffracting device is a polarization hologramwhose diffracting function is different according to polarization stateof the incident light beam, and includes plural polarization hologramportions configured to diffract the light beams of different wavelengthsreflected from the optical device with reflecting portion to the photodetecting device for monitor light detection. Therefore, with respect toeach of light beams of plural wavelengths, diffracting efficiency can beimproved, flare light can be reduced, and monitor light detection andsignal light detection can be more sensitive.

According to another aspect of the present invention, in an opticalpickup apparatus, a section of the diffracting device at a side of theoptical device with a reflecting portion is formed in bilateralasymmetry. Therefore, intensity of a light beam which is guided to aphotodetecting device within diffracting lights of ± first order can belarge, and signal to noise ratio of monitor light detection and signallight detection can be improved, and a flare light can be reduced.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. An optical pickup apparatus for reading/reproducing data on anoptical recording medium, comprising: a light source configured to emita light beam; a diffracting device configured to transmit the light beamemitted from the light source, and to diffract a light beam reflectedfrom the optical recording medium; an optical device having a reflectingportion and a transmitting portion, configured to reflect one part ofthe light beam emitted from the light source to the diffracting deviceby the reflecting portion and to transmit another part of the light beamemitted from the light source to the optical recording medium by thetransmitting portion, and to transmit the light beam reflected from theoptical recording medium to the diffracting device by the transmittingportion; a photodetecting device configured to detect the light beamreflected from the optical recording medium through the optical deviceand the diffracting device, for signal light detection; and wherein thediffracting device includes a diffracting portion to diffract the onepart of the light beam reflected by the reflecting portion of theoptical device to the photodetecting device for monitor light detectionof the light source.
 2. The optical pickup apparatus of claim 1, whereinthe diffraction device is a transmitting type diffraction device.
 3. Theoptical pickup apparatus of claim 1, wherein the optical device isintegrated with the diffracting device.
 4. The optical pickup apparatusof claim 1, wherein the diffracting device is a polarization hologramwhose diffracting function is different according to a polarizationstate of the incident light beam, and includes a polarization hologramportion configured to diffract the light beam reflected from the opticaldevice to the photodetecting device for monitor light detection.
 5. Anoptical pickup apparatus for reading/reproducing data on an opticalrecording medium, comprising: light sources configured to emit lightbeams of different wavelengths; a diffracting device configured totransmit the light beams emitted from the light sources and to diffractlight beams reflected from the optical recording medium; an opticaldevice having a reflecting portion and a transmitting portion,configured to reflect one part of the light beams emitted from the lightsources to the diffracting device by the reflecting portion and totransmit other parts of the light beams emitted from the light sourcesto the optical recording medium by the transmitting portion, and totransmit the light beams reflected from the optical recording medium tothe diffracting device by the transmitting portion; a photodetectingdevice configured to detect the light beams reflected from the opticalrecording medium through the optical device with reflecting portion andthe diffracting device, for signal light detection; and wherein thediffracting device includes plural diffracting portions, in which eachof the diffracting portions corresponds to one of the differentwavelengths, to diffract the respective parts of the light beamsreflected by the reflecting portion of the optical device to thephotodetecting device, so as to be detected on the photodetecting devicefor monitor light detection of each of the light sources.
 6. (Cancelled)7. The optical pickup apparatus of claim 5, wherein the optical deviceis integrated with the diffracting device.
 8. The optical pickupapparatus of claim 5, wherein the diffracting device is a polarizationhologram whose diffracting function is different according to apolarization state of the incident light beam, and includes pluralpolarization hologram portions configured to diffract the light beams ofthe different wavelengths reflected from the optical device to thephotodetecting device for monitor light detection.
 9. The optical pickupapparatus of claim 3 or claim 7, wherein a section of the diffractingdevice at a side of the optical device forms a section of bilateralasymmetry.
 10. An optical pickup apparatus for reading/reproducing dataon an optical recording medium, comprising: light emitting means foremitting a light beam; diffracting means for transmitting the light beamemitted from the light emitting means, and for diffracting a light beamreflected from the optical recording medium; optical means having areflecting portion and a transmitting portion, for reflecting one partof the light beam emitted from the light emitting means to thediffracting means by the reflecting portion and for transmitting anotherpart of the light beam emitted from the light emitting means to theoptical recording medium by the transmitting portion, and fortransmitting the light beam reflected from the optical recording mediumto the diffracting means by the transmitting portion; detecting meansfor detecting the light beam reflected from the optical recording mediumthrough the optical device with reflecting portion and the diffractingdevice, for signal light detection; and wherein the diffracting deviceincludes a diffracting portion to diffract the one part of the lightbeam reflected by the reflecting portion of the optical means to thedetecting means for monitor light detection of the light emitting means.11. An optical pickup apparatus for reading/reproducing data on anoptical recording medium, comprising: light emitting means for emittinglight beams of different wavelengths; diffracting means for transmittingthe light beams emitted from the light emitting means and fordiffracting light beams reflected from the optical recording medium;optical means having a reflecting portion and a transmitting portion,for reflecting parts of the light beams emitted from the light emittingmeans to the diffracting means by the reflecting portion, and fortransmitting other parts of the light beams emitted from the lightemitting means to the optical recording medium by the transmittingportion, and for transmitting the light beams reflected from the opticalrecording medium to the diffracting means by the transmitting portion;detecting means for detecting the light beams reflected from the opticalrecording medium through the optical device and the diffracting device,for signal light detection; and wherein the diffracting means includesplural diffracting portions, in which each of the diffracting portionscorresponds to one of different wavelengths of said light beams, todiffract the parts of the light beams reflected by the reflectingportion of the optical means to the detecting means, so as to bedetected on the detecting means for monitor light detection of each ofthe light emitting means.
 12. An optical data recording/reproducingapparatus for recording/reproducing data on an optical recording medium,comprising: a light source configured to emit a light beam; adiffracting device configured to transmit the light beam emitted fromthe light source, and to diffract a light beam reflected from theoptical recording medium; an optical device having a reflecting portionand a transmitting portion, configured to reflect one part of the lightbeam emitted from the light source to the diffracting device by thereflecting portion and to transmit another part of the light beamemitted from the light source to the optical recording medium by thetransmitting portion, and to transmit the light beam reflected from theoptical recording medium to the diffracting device by the transmittingportion; a collimating lens configured to collimate the light beamtransmitted through the transmitting portion of the optical device withreflecting portion; an objective lens configured to focus the light beamfrom the collimating lens onto the optical recording medium; aphotodetecting device configured to detect the light beam reflected fromthe optical recording medium through the objective lens, the collimatinglens, the optical device, and the diffracting device, for signal lightdetection; and wherein the diffracting device includes a diffractingportion to diffract the one part of the light beam reflected by thereflecting portion of the optical device to the photodetecting device,so as to be detected on the photodetecting device for monitor lightdetection of the light source.
 13. An optical data recording/reproducingapparatus for recording/reproducing data on an optical recording medium,comprising: light sources configured to emit light beams of differentwave lengths; a diffracting device configured to transmit the lightbeams emitted from the light sources and to diffract light beamsreflected from the optical recording medium; an optical device having areflecting portion and a transmitting portion, configured to reflectparts of the light beams emitted from the light sources to thediffracting device by the reflecting portion, and to transmit otherparts of the light beams emitted from the light sources to the opticalrecording medium by the transmitting portion, and to transmit the lightbeams reflected from the optical recording medium to the diffractingdevice by the transmitting portion; a collimating lens configured tocollimate the light beams transmitted through the transmitting portionof the optical device; an objective lens configured to focus the lightbeams from the collimating lens onto the optical recording medium; aphotodetecting device configured to detect the light beams reflectedfrom the optical recording medium through the objective lens, thecollimating lens, the optical device and the diffracting device, forsignal light detection; and wherein the diffracting device includesplural diffracting portions, in which each of the diffracting portionscorresponds to one of different wavelengths of the light beams, todiffract the respective parts of the light beams reflected by thereflecting portion of the optical device to the photodetecting device,so as to be detected on the photodetecting device for monitor lightdetection of each of the light sources.
 14. An optical datarecording/reproducing apparatus for recording/reproducing data on anoptical recording medium, comprising: light emitting means for emittinga light beam; diffracting means for transmitting the light beam emittedfrom the light emitting means, and for diffracting a light beamreflected from the optical recording medium; optical means having areflecting portion and a transmitting portion, for reflecting one partof the light beam emitted from the light emitting means to thediffracting means by the reflecting portion and for transmitting anotherpart of the light beam emitted from the light emitting means to theoptical recording medium by the transmitting portion, and fortransmitting the light beam reflected from the optical recording mediumto the diffracting device by the transmitting portion; collimating meansfor collimating the light beam transmitted through the transmittingportion of the optical means; focusing means for focusing the light beamfrom the collimating means to the optical recording medium; detectingmeans for detecting the light beam reflected from the optical recordingmedium through the collimating means, the focusing means, the opticalmeans, and the diffracting means, for signal light detection; andwherein the diffracting means includes a diffracting portion to diffractthe part of the light beam reflected by the reflecting portion of theoptical means to the detecting means, so as to be detected on thedetecting means for monitor light detection of the light emitting means.15. An optical data recording/reproducing apparatus forrecording/reproducing data on an optical recording medium, comprising:light emitting means for emitting light beams of different wave lengths;diffracting means for transmitting the light beams emitted from thelight emitting means and for diffracting light beams reflected from theoptical recording medium; optical means having a reflecting portion anda transmitting portion, for reflecting parts of the light beams emittedfrom the light emitting means to the diffracting means by the reflectingportion and for transmitting other parts of the light beams emitted fromthe light emitting means to the optical recording medium by thetransmitting portion, and for transmitting the light beams reflectedfrom the optical recording medium to the diffracting means by thetransmitting portion; collimating means for collimating the light beamstransmitted through the transmitting portion of the optical means withreflecting portion; focusing means for focusing the light beams from thecollimating means to the optical recording medium; detecting means fordetecting the light beams reflected from the optical recording mediumthrough the collimating means, the focusing means, the optical means,and the diffracting means, for signal light detection; and wherein thediffracting means includes plural diffracting portions, in which each ofthe diffracting portions corresponds to one of different wavelengths ofthe light beams, the respective light beams reflected by the reflectingportion of the optical means to the detecting means, so as to bedetected on the detecting means for monitor light detection of each ofthe light emitting means.
 16. An optical data recording/reproducingmethod for recording/reproducing data on an optical recording medium,comprising: emitting a light beam by a light source; transmitting thelight beam emitted from the light source and diffracting a light beamreflected from the optical recording medium by a diffracting device;reflecting one part of the light beam emitted from the light source tothe diffracting device by a reflecting portion of an optical device andtransmitting another part of the light beam emitted from the lightsource to the optical recording medium by a transmitting portion of theoptical device, and transmitting the light beam reflected from theoptical recording medium to said diffracting device by the transmittingportion of the optical device; collimating the light beam transmittedthrough the transmitting portion of the optical device by a collimatinglens; focusing the light beam from the collimating lens to the opticalrecording medium by an objective lens; detecting the light beamreflected from the optical recording medium through the objective lens,the collimating lens, the optical device, and the diffracting device,for signal light detection by a photodetecting device; and diffractingthe part of the light beam reflected by the reflecting portion of theoptical device to the photodetecting device, so as to be detected on thephotodetecting device for monitor light detection of the light source.17. The method according to claim 16 further comprising using saidphotodetecting device to control output of said light source.
 18. Anoptical data recording/reproducing method for recording/reproducing dataon an optical recording medium, comprising: emitting light beams ofdifferent wavelengths by light sources; transmitting the light beamsemitted from the light sources and diffracting light beams reflectedfrom the optical recording medium by a diffracting device; reflectingparts of the light beams emitted from the light sources to thediffracting device by a reflecting portion of an optical device andtransmitting other parts of the light beams emitted from the lightsource to the optical recording medium by a transmitting portion of theoptical device, and transmitting the light beams reflected from theoptical recording medium to said diffracting device by the transmittingportion of the optical device; collimating the light beams transmittedthrough the transmitting portion of the optical device by a collimatinglens; focusing the light beams onto the optical recording medium by anobjective lens; detecting the light beams reflected from the opticalrecording medium through the objective lens, the collimating lens, theoptical device, and the diffracting device, for signal light detectionby a photodetecting device; and diffracting light beams reflected by thereflecting portion of the optical device to the photodetecting devicethrough plural diffracting portions, in which each of the diffractingportions corresponds to one of the different wavelengths, so as to bedetected on the photodetecting device for monitor light detection ofeach of the light sources.
 19. The method according to claim 18 furthercomprising using said photodetecting device to control output of saidlight source.
 20. The optical pickup apparatus of claim 1, wherein thediffracting device includes at its center portion a portion to diffractsaid light beam emitted from the light source, and further includes atits peripheral portion said diffracting portion to diffract said onepart of the light beam reflected by the reflecting portion.
 21. Theoptical pickup apparatus of claim 1, further comprising a quarter waveplate disposed between said optical device and said diffracting device.22. The optical pickup apparatus of claim 1, further comprising a secondphotodetecting device for receiving only said one part of the light beamreflected by the reflecting portion of the optical device.
 23. Anoptical pickup apparatus for reading/reproducing data, comprising: alight source configured to emit a light beam; a diffracting deviceconfigured to transmit the light beam emitted from the light source, andto diffract a light beam reflected from the optical recording medium; anoptical device having a reflecting portion and a transmitting portion,configured to reflect one part of the light beam emitted from the lightsource to the diffracting device by the reflecting portion and totransmit another part of the light beam emitted from the light source tothe optical recording medium by the transmitting portion, and totransmit the light beam reflected from the optical recording medium tothe diffracting device by the transmitting portion; a photodetectingdevice configured to detect the light beam reflected from the opticalrecording medium through the optical device and the diffracting device,for signal light detection; and wherein the diffracting device includesa diffracting portion to diffract the one part of the light beamreflected by the reflecting portion of the optical device to thephotodetecting device for monitor light detection of the light source,and said signal light detection signals and said monitor light detectionsignals are transmitted through a transmissive hologram.